<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>类选择器</title>
    <style>
        .want {
            color: red;
        }

        .disgust {
            color: green;
        }

        .R {
            background: red;
            width: 250px;
            height: 250px;

        }
.B {
    background: blue;
            width: 250px;
            height: 250px;
}


    </style>
</head>
<body>
   <ul>
    <li>火锅</li>
    <li class="want">烧烤</li>
    <li>炒菜</li>
    <li class="want">烤肉</li>
    <li>甜品</li>
    <li class="disgust">糖水</li>
   </ul> 

   <div class="R"></div>
   <div class="B"></div>
   <div class="R"></div>
</body>
</html>